might be a dumb question.....
At idle and cruising around, your car will actually be leaner due to the long tubes. This is due to the O2 sensors being moved downstream and not functioning as well in that new location. Your PCM will try to correct for this by sending the fuel trims in the + direction.
The + trims will in turn drive you rich at WOT, since the computer wants the safest possible operation of the car (i.e. - it needs more fuel driving around town, so it must need even more at WOT).
LTs are a tuning nightmare in closed loop operation.





